VMWARE ESXI configureation

Posted on 2014-07-15
Last Modified: 2014-07-15
I inherited few vmware servers.  They're 4  quad xeon servers with hyperthreading and 64 gb of RAM.  The ESXI is an enterprised version.   Some of the VM's are configured with 8 virtual processors and 8-24 gb of ram.  About 8 VMs are running on each host.  Are there advantages of using over 2 virtual processors?   Is it necessary to allocate 24 gb of Ram to virtual machine.
Question by:jem1662
    LVL 116

    Expert Comment

    by:Andrew Hancock (VMware vExpert / EE MVE)
    Your VMs seem to hive too many vCPUs allocated.

    Very often you do not need more than 2 vCPUs

    Author Comment

    Are the best practice for virtual processors and guest memory usage?
    LVL 3

    Expert Comment

    What Software is installed inside the VM's ?

    Author Comment

    Windows 2008 R2 Server,  some vms have small sql server database,  some have oracle and one vm has a product called QLIKVIEW.
    LVL 116

    Accepted Solution

    vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectly, e.g. Servers than can use vSMP correctly :- SQL Server, Exchange Server.

    This is true, many VMware Administrators, think adding lots of processors, will increase performance - wrong! (and because they can, they just go silly!). Sometimes there is confusion between cores and processors. But what we are adding is additional processors in the virtual machine.

    So 4 vCPU, to the VM is a 4 Way SMP (Quad Processor Server), if you have Enterprise Plus license you can add 8, (and only if you have the correct OS License will the OS recognise them all).

    If applications, can take advantage e.g. Exchange, SQL, adding additional processors, can/may increase performance.

    So usual rule of thumb is try 1 vCPU, then try 2 vCPU, knock back to 1 vCPU if performance is affected. and only use vSMP if the VM can take advantage.

    Example, VM with 4 vCPUs allocated!

    My simple laymans explaination of the "scheduler!"

    As you have assigned 4 vCPUs, to this VM, the VMware scheulder, has to wait until 4 cores are free and available, to do this, it has to pause the first cores, until the 4th is available, during this timeframe, the paused cores are not available for processes, this is my simplistic view, but bottom line is adding more vCPUs to a VM, may not give you the performance benefits you think, unless the VM, it's applications are optimised for additional vCPUs.

    See here

    see here

    also there is a document here about the CPU scheduler

    As for RAM allocation in the VM, is it necessary, how much is in could reduce it, at no performance decrease, but check your performance.

    Author Closing Comment

    Thank You for the info.

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